1. Field of the Invention
The present invention relates to a magnetic head for use in a floppy disc drive (FDD) and a hard disc drive (HDD).
2. Description of the Related Art
An example of a conventional magnetic head that is used in an FDD is shown in FIG. 10.
In FIG. 10, a magnetic head 1xe2x80x2 is, in general, composed of a slider 2 sliding on a magnetic recording medium (not shown), a substantially rectangular opening 3 formed in the slider 2, a magnetic core 6 having gaps (a read/write gap 4 and an erasing gap 5), inserted into the opening 3 and sealed up with a sealing material such as glass, a back yoke 7 made of a magnetic material and joined to the magnetic core 6 to thereby form a closed magnetic path, and a read/write coil 11 and an erasing coil 12 respectively provided on leg portions 8, 10 of the back yoke 7.
The magnetic core 6, which is inserted in the opening 3 formed in the slider 2, is sealed up with glass, etc. which is molten and poured into gaps formed between the magnetic core 6 and inner walls of the slider 2 in order to prevent it from happening that foreign substances like dusts get in the gaps and deteriorate characteristics.
The slider 2 including the opening 3 is formed by press-molding and then sintering. However, the opening 3 formed with this method does not always have a precise rectangular shape. As shown in FIG. 11, the opening 3 may be deformed in such a manner as to have an increased width at the middle or its longitudinal direction (FIG. 11) or a decreased width to the contrary. The magnetic core 6 inserted in the opening 3 with such a deformation is apt to move freely when molten glass is poured thereinto, making it difficult to determine an appropriate position of the magnetic core 6.
FIG. 12 shows an embodiment in which projections 30a, 31a and 31b are provided on some of the inner walls of the opening 3 as a means for locating the magnetic core 6 at an appropriate position.
Of four inner walls 30, 31, 32 and 33, which define the opening 3, the inner wall 30 is provided at its middle with the projection 30a extending in a depth direction (in a direction perpendicular to the paper of FIG. 12) of the opening 3. The inner wall 31 is provided with the two projections 31a, 31b having the same height as the projection 30a and extending in a depth direction of the opening 3 like the projection 30a. 
In a magnetic head shown in FIG. 12, when molten glass is poured into the opening 3, gaps between the magnetic core 6 and the inner walls 30, 31 provided with the projections 30a, 31a, 31b are to receive more molten glass than those between the magnetic core 6 and the inner walls 32, 33 provided with no projection. Accordingly, there is generated an imbalance of surface tension in the poured glass, and the magnetic core 6 is moved toward the inner walls 32, 33 to be duly positioned. However, the amount of glass poured between the magnetic core 6 and the inner walls 30, 31 provided with the projections 30a, 31a, 31b is different from the amount of glass poured between the magnetic core 6 and the inner walls 32, 33 provided with no projection. Therefore, if the viscosity of the glass is smaller than the optimum, the glass is too fluid and may flow out in an undesirable way when poured between the magnetic core 6 and the inner walls 30, 31. On the other hand, if the viscosity of the glass is larger than the optimum, the glass may not satisfactorily flow between the magnetic core 6 and the inner walls 32, 33.
In order to solve such problems, a magnetic head shown in FIG. 13 is provided with projections 32a, 33a, 33b on the inner walls 32, 33, which are located to oppose respectively the projections 30a, 31a, 31b on the inner walls 30, 31. According to this magnetic head, the glass can be easily poured between all the inner walls 30 to 33 and a magnetic core 6. However, it is still impossible to determine an appropriate position of the magnetic core 6 because there are gaps existing between the respective projections and the magnetic core 6, in other words, the width and length of the magnetic core 6 are different from the distances between the projections 31a and 33a, and 31b and 33b and between the projections 30a and 32a, respectively.
Now, in a magnetic head shown in FIG. 14, of projections provided on the four inner walls 30 to 33, projections 30axe2x80x2, 33axe2x80x2 and 33bxe2x80x2 on the inner walls 30 and 33 are formed such that their heights from the inner walls are smaller than those of the projections 31a, 31b and 32a on the inner walls 31 and 32. With this formation, when glass is poured into an opening 3, the glass is to flow in a larger amount into gaps between the magnetic core 6 and the inner wall 31 provided with higher projections and between the magnetic core 6 and the inner wall 32 provided with a higher projection, than into gaps between the magnetic core 6 and the inner wall 30 provided with a lower projection and between the magnetic core 6 and the inner wall 33 provided with lower projections. Therefore, a difference is generated in surface tension of the glass, and the magnetic core 6 is moved toward the inner walls 30 and 33. As a result, the magnetic core 6 at one side is aligned to the heights of the projections 30axe2x80x2, 33axe2x80x2 and 33bxe2x80x2 to be duly positioned. Since the projections 30axe2x80x2, 33axe2x80x2 and 33bxe2x80x2 exist on the inner wall 30 and 33, toward which the magnetic core 6 is moved, gaps are secured between the inner walls 30 and 33 and the magnetic core 6, thereby allowing the glass to appropriately flow.
In a composite type magnetic head for an HDD, a metal spacer maybe used as a means of positioning a magnetic core. For instance, a thin plate spring made of phosphorous bronze, beryllium copper or the like is put as a spacer between the magnetic core and the inner walls or the opening to determine an appropriate position of the magnetic core. However, the thermal expansion coefficient of metal as a spacer is greatly different from that of the glass to be poured in the opening to seal up the magnetic core, so cracks are easily generated in the glass. Further, if the metal used as a spacer is exposed at a surface sliding on a recording medium, since the hardness of the metal is lower than that of the glass and of ceramics as a magnetic core material, the metal part is worn away more quickly due to friction, which causes a partial abrasion in the slider. As a result, there is a deterioration easily generated with regard to a contact with a recording medium and a posture thereto.
As a density of a recording medium becomes higher, it is required to increase a track density in order to increase a writing capacity of a unit track, forcing its track width to be decreased. While this reduces the thickness of a magnetic core contributing to cost reduction, the wall thickness of a molding die for a slider into which the magnetic core is inserted has to be also reduced creating problems with the strength and life of the molding die. Specifically in a magnetic head for a high recording density FDD of 120 MB type, its track width is about 8 xcexcm, so the thickness of the magnetic core is about 0.08 to 0.1 mm. This means the magnetic head is about xc2xd as thick as a magnetic head for a standard recording density FOD of 2 MB type. Further, if the thickness of the magnetic core is reduced, it becomes accordingly possible to reduce (narrower) the size of the opening of the slider formed to accept the magnetic core. However, for making the opening of the slider narrower, it is necessary to reduce the thickness of a molding die for forming the opening, whereby the molding die can be easily deformed. This makes it difficult to keep the same precision in the shape of the opening that has been available. The resultant deformation of the opening increases a variation in the accuracy of positioning the magnetic core in the opening. If the projections formed on the inner walls of the opening are set higher while the opening is kept of same size as the opening conventionally sized, a space to be filled with glass, that is, a gap between the inner wall of the opening and the magnetic core is increased, and an increased amount of glass is poured in the opening to seal up the magnetic core. Accordingly, there is more chance for bubbles to be generated in the glass, and also an increased number of stepped portions are generated on the glass due to abrasion by other substances during manufacturing process and the stepped portions may hold fine particles formed by the sliding of the slider on the recording medium, thereby generating a clearance larger than necessary between the magnetic core and the recording medium, which causes a decrease in the output of the magnetic head and damages to the recording medium. And, if the groove of a track is made deeper to meet a higher density of the recording medium while the opening is kept of same size as the opening conventionally sized and the thickness of the magnetic core is kept identical with that of the conventional one, glass is poured in the deeper groove in the process of manufacturing the magnetic core increasing the area filled with glass. So, there are generated same problems as found in the case where the projections on the inner wall of the opening are set higher.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic head which enables a smooth flow of glass poured into an opening for sealing up the magnetic core, whereby a magnetic core can be easily and accurately positioned.
In order to solve the above problems, according to a first aspect of the present invention, in a magnetic head comprising a slider opposing a magnetic recording medium, a substantially rectangular opening formed in the slider and a magnetic core inserted in the opening and sealed up therein with a sealing material, the magnetic core is positioned by a spacer made of a material equivalent to that of the slider in thermal expansion coefficient, and the spacer is exposed at a sliding surface of the slider sliding on the magnetic recording medium.
According to a second aspect of the present invention, in the magnetic head according to the first aspect, the spacer is made of the same material that the slider is made of.
According to a third aspect of the present invention, in the magnetic head according to the first or second aspect, a plurality of projections are provided on an inner wall of one longitudinal side of the opening, and the magnetic core is disposed between the spacer and the projections in such a manner as to contact with the projections.
According to a fourth aspect of the present invention, in the magnetic head according to the first or second aspect, each spacer is disposed at both sides of the magnetic core.
According to a fifth aspect of the present invention, in the magnetic head according to the third or fourth aspect, the spacer has a bulge with an increased thickness at one or both ends in the longitudinal direction thereof.
According to a sixth aspect of the present invention, in the magnetic head according to any one of the third to fifth aspects, the spacer has a wedge-shaped section tapering off toward the direction of insertion into the opening.
According to a seventh aspect of the present invention, in the magnetic head according to any one of the first to fourth aspects, the spacer has a step portion with a reduced thickness forming a tenon shape in section at one end in the direction of insertion, and is inserted in the opening in such a manner that the one end with the step portion with a reduced thickness is positioned toward the sliding surface of the slider.